Function generator



FUNCTION GENERATOR Walter R. Hedeman, Jr., Baltimore, Md., assignor toBendix Aviation Corporation, Towson, Md., a corporation of DelawareApplication September 18, 1951, Serial No. 247,046

2 Claims. (Cl. 250-27) This invention relates generally to electricfunction generation and more particularly to circuits for generatinginverse functions related to a mechanical motion.

Many function generators are known in the art for producing desiredmathematical relationships between physical quantities. Theestablishment of a desired inverse functional relationship between twoquantities has in the past been accomplished with relatively complexarrangements.

The primary object of the present invention is to provide a simple andeconomical inverse function generator.

Another object is to provide an improved function generator which isstable in operation and capable of supplying useful load current.

A further object resides in provision for adjusting the shape andrelative position of the inverse function generated to satisfy varyingrequirements. I

These and other objects of the invention are achieved by providing acontrolled output voltage across an output impedance element which isunder control of the voltage across a portion of the impedance. Circuitarrangements are provided whereby the control voltage across the portionof the impedance is maintained substantially constant regardless of theratio that portion bears to the whole output impedance so long as thecontrol range is not exceeded. Under these conditions'motion imparted toa variable element to vary the ratio the portion bears to the wholegenerates as the controlled output voltage an inverse analogue of themotion.

In the drawings:

Fig. l is a schematic diagram of a circuit of the present inventionemployed in an antenna system;

Fig. 2 shows a modification; and

Fig. 3 is a schematic diagram of a circuit of the invention havingsensitivity and level adjustments.

Referring to Fig. 1 there is shown a variable width waveguide antenna 11having a movable element 12 driven in oscillatory linear motion by adriving means 13. A current supply tube 14 supplies current to theseries adjustable resistors R1, R2 and R3 from a D. C. source 15. Thehigh potential end of R1 is connected to control a suitably referencedamplifier tube 16 which in turn controls the current tube 14. The valueof R1 is varied in accordance with the position of the element 12 by asuitable linkage thereto. The output voltage e appearing across R1, R2and R3 is applied to a utilization means such as a deflection circuit 17of a cathode-ray tube 18.

In operation the linear movement of the element 12 causes a scanningmotion of the beam of the antenna 11 which is related to thedisplacement of element 12 by a hyperbolic or inverse function. Thelinear motion (translational or angular) which varies the resistance ofR1 linearly, produces an output voltage 20 which can be made theanalogue of the scanning antenna beam position as follows. The gainprovided by control tube 16 is made sufiiciently high to maintain thevoltage 21 essentially constant regardless of the setting of R1 Withinthe nited States Patent O Patented Sept. 20, 1955 ice operating range ofthe system. For this condition the output voltage is which variesinversely with the value of R1. This is a general form of an expressionfor a hyperbolic function which can be made to fit a given hyperbola byadjustment of the parameters R2 and R3 and the addition of a D. C.voltage for level adjustment, if required. The phase of the change in R1with respect to the antenna beam motion (i. e. whether R1 increases ordecreases With respect to beam motion from an arbitrarily chosen zeroposition) determines the sign of the functional relationship between thedependent and independent variables.

In applications where the hyperbolic term is desired free of theconstant term (:21), the voltage eh may be utilized as the outputvoltage. This arrangement will, in general, be limited to small loadcurrents to prevent any appreciable voltage drop in R3 therefrom.

Referring to Fig. 2 a modification of the voltage divider R1, R2, R3 isshown in which R1 is constant and at is established across R3 and afractional part of R1, namely, XR1 where X has values between zero andunity. The resultant expressions for so and en are again hyperbolic andof the form and In Fig. 3 a modification is shown in which R3 is made upof two series resistances Rz-l-R4. For this arrangement the expression(1) becomes which may be a more convenient form for adjusting theparameters to obtain a fit with a given curve. The two resistors ofvalue R2 in Fig. 3 are ganged to maintain their equality for allsettings. The cathode of tube 16 in Fig. 3 is returned to a source ofadjustable reference potential E such as an independent regulated D. C.supply 21 to provide a sensitivity adjustment controlling the availableoutput voltage swing of as. The D. C. level of 20 is adjusted to anydesired value by returning the voltage divider via lead 22 to apotential Ec from another suitable independent D. C. voltage source suchas regulated supply 23.

The operation of the circuit of Fig. 3 in a particular case would be asfollows. In an application, such as a cathode-ray tube deflectioncircuit drive, it is desired to drive the deflection stage from nearcutoff to near gridcurrent voltage levels. This implies a specificvoltage range of swing between specific voltage levels. The proper shapecurve to fit the analogue is obtained by the choice of values of R1, R2,R4, using curve fitting techniques such as obtaining a fit at two ormore points by substituting values for the variables at three points andsolving for the unknown values. The amplitude of voltage change isadjusted by adjusting the voltage E, since this is a sensitivitycontrol. The level at which the swing starts is then set by adjustingEC, which is a bias or level control. The output of the device is thenthe desired form of signal for the particular case under consideration.

Obviously, other degenerative amplifier systems may be used to drive theoutput impedance combination. Such amplifiers need only to maintainsubstantially constant the voltage across the portion of the outputimpedance which supplies the input thereof for the purpose of thisinvention.

What is claimed is:

1. A system for producing a voltage which is an inverse function of alinear mechanical motion input, comprising: a constant voltage directcurrent source; positive and negative terminals associated with the saidsource;

a triode vacuum tube; means electrically connecting the plate of thesaid tube to the said positive terminal; three resistors; an elementassociated with one of the said resistors to vary the value of theresistance thereof; said resistors being serially and electricallyconnected such that the said variable resistor is located in the centerposition thereof; means electrically connecting the said seriallyconnected resistors between the cathode of the said tube and the saidnegative terminal; an amplifying tube; a fourth resistor; meanselectrically connecting the said fourth resistor between the plate ofthe said amplifying tube and the said positive terminal; a biasingmeans; said biasing means electrically connected between the cathode ofthe said amplifying tube and the said negative terminal; meanselectrically connecting the said plate of the said amplifying tube tothe grid of the said triode tube; means electrically connecting the gridof the said amplifying tube to the terminal of said variable resistorthat is electrically closer to the said cathode of the said triode tube;and means imparting a mechanical motion to said element to vary thevalue of the said variable resistor thereby producing a voltagevariation across the said serially connected resistors which is aninverse function of the said mechanical motion.

2. A system for producing a voltage which is an inverse function of alinear mechanical motion input, comprising: a constant voltage directcurrent source; positive and negative terminals associated with saidsource; a vacuum tube having a plate, a cathode and at least one grid;means electrically connecting the plate of said tube to the saidpositive terminal; a resistance voltage divider having an intermediatepoint movable over a range of values for changing the ratio of theresistances of said divider on opposite sides of said point; meanselectrically connecting the said voltage divider between the cathode ofsaid tube and the said negative terminal; an amplifying tube having aplate, a cathode and at least one grid; a resistor; means electricallyconnecting the said resistor between the plate of the said amplifyingtube and the said positive terminal; a biasing means; said biasing meanselectrically connected between the cathode of said amplifying tube andthe said negative terminal; means electrically connecting the said plateof said amplifying tube to the grid of said vacuum tube; meanselectrically connecting the grid of Said amplifying tube to said movablepoint; and means imparting a mechanical motion to the said movable pointto produce a voltage variation across said voltage divider which is aninverse function of said mechanical motion.

References Cited in the file of this patent UNITED STATES PATENTS2,268,790 White Ian. 6, 1942 2,398,916 Brewer Apr. 23, 1946 2,407,458Spielman Sept. 10, 1946 2,409,456 Tolson Oct. 15, 1946 2,461,514 BowersFeb. 15, 1949 2,483,644 Kelsey Oct. 4, 1949 2,510,687 DeVore June 6,1950 2,525,698 Mackenzie Oct. 10, 1950 2,527,753 McConnell Oct. 31, 19502,567,880 Frommer Sept. 11, 1951

